The present invention relates to turbines, for example, land-based gas turbines having nozzle stages and particularly to a guide tube for a thermocouple wire extending through a vane of the nozzle stage containing a thermal cooling medium.
In turbines, particularly land-based gas turbines, it is desirable to monitor the temperature of the wheelspaces between the wheels and diaphragms. Thermocouple wires may extend through one of the nozzle vanes for mounting the thermocouple sensor probe to measure the temperature of the wheelspace. The thermocouple wires are typically encased in tubes to ensure the integrity of the wire throughout the life of the turbine.
In advanced gas turbines, however, a thermal cooling medium flows through the nozzle vanes of the various nozzle stages for cooling the nozzle surfaces exposed to the hot gas path. The preferred cooling medium in one such advanced gas turbine is steam. The steam flows into a plenum between an outer cover and an outer band of a nozzle stage for flow through an impingement plate for impingement-cooling of the outer band surfaces. Spent impingement steam flows through openings into vane extensions for flow radially inwardly through the vane. Typically, inserts are employed within the nozzle vane cavities which receive the cooling flow and pass the cooling flow through openings in the inserts for impingement-cooling of the surfaces of the nozzle vanes. The spent impingement-cooling steam then flows radially inwardly into a plenum between the inner cover and the inner band for flow through openings in an impingement plate for impingement-cooling of the inner band surfaces. The spent cooling medium then returns through one of the cavities of the nozzle vane and through the outer band and cover.
When using a thermal cooling medium such as steam, it is vital that the steam does not leak into the wheelspace areas or the hot gas path, as well as other areas within the turbine. A problem, however, develops when a thermocouple wire is extended within a guide tube through a nozzle vane carrying a thermal cooling medium. Because of a thermal responsive mismatch between the thermocouple guide tube, for example, a straight, linearly extending tube housing the thermocouple wire and fixed opposite ends of the thermocouple guide tube, the tube will not accommodate movement responsive to the thermal cooling medium. Moreover, the tube must also be sealed to prevent leakage of the cooling medium.
In accordance with a preferred embodiment of the present invention, a non-linearly extending tube housing the thermocouple wire extends through sleeves fixed and sealed to the outer and inner covers, respectively. The tube is likewise fixed and sealed to the sleeves. To accommodate thermal expansion and contraction of the tube, the tube is non-linear in shape and thus flexes between the outer and inner covers. More particularly, the tube is serpentine in configuration to accommodate the thermal movement. Additionally, the cavity within the nozzle vane through which the guide tube extends has an insert for facilitating impingement-cooling of the surface of the nozzle vane. To accommodate the thermocouple guide tube and its thermally responsive movement within the cavity, the insert has a pair of chambers adjacent suction and pressure sides of the vane. The inserts have openings through walls thereof for impingement-cooling of the suction and pressure surfaces of the nozzles. The interior walls of the insert defining the chambers are spaced from one another and are preferably connected by a pair of side walls defining a central chamber through the insert. Apertures, preferably elongated, are formed through the side walls to receive serpentine portions of the guide tube. Thus, the guide tube extends from the outer cover through the outer band into the central chamber of the insert, outwardly through an aperture in one wall of the central chamber and then returns into the central chamber for extension through an aperture in the opposite wall and return into the central chamber. The tube then extends through the inner band and the inner cover.
In accordance with a preferred embodiment of the present invention, the guide tube is fixed to the inner and outer covers. This is accomplished preferably by; fixing and sealing, e.g., welding, the tube end portions in sleeves in turn fixed and sealed to the covers. Thus, the serpentine configuration of the guide tube facilitates expansion and contraction of the guide tube within the nozzle vane and between the mounting sleeves while leakage of cooling medium is precluded by the seal between the tube and sleeves and sleeves and covers at radial inner and outer end portions of the nozzle.
In a preferred embodiment according to the present invention, there is provided in a turbine having stages including a fixed nozzle stage segment having inner and outer bands, a plurality of nozzle vanes extending between the inner and outer bands, and inner and outer covers overlying the inner and outer bands, respectively, apparatus for guiding a thermocouple through the fixed stage, comprising a tube extending through the outer cover, the outer band, a nozzle vane of the fixed nozzle stage, the inner band and the inner cover, a thermocouple wire within the tube, the tube extending non-linearly through the nozzle vane and fixed at opposite ends to the outer cover and the inner cover, respectively, the tube being responsive to temperature variations to expand and contract within the nozzle vane while remaining fixed at opposite ends thereof to the outer and inner covers.